The present invention relates to a hydrogenation catalyst for aromatic hydrocarbons contained in hydrocarbon oils, and relates particularly to a hydrogenation catalyst for aromatic hydrocarbons contained in hydrocarbon oils which has a low hydrocracking ratio, high resistance to poisoning by sulfur hydrocarbons and the like, and high hydrogenation activity.
The light gas oil used for fuel in diesel engines is prepared as a blend of mainly a light gas oil obtained by performing hydrodesulfurization and denitrogentation processing on a straight run light gas oil fraction having a specific boiling point range obtained by atmospheric distillation of crude oil, and a light gas oil fraction obtained by vacuum distillation.
However, because the volume of the light gas oil fraction in the crude oil is limited, and crude oil becomes heavier over time, the straight run light gas oil fraction obtained by atmospheric distillation tends to reduce in volume. Furthermore, because the demand for light gas oil is increasing in accordance with an increase in the production of diesel engines, a shortage in the supply of light gas oil is anticipated in the near future.
As a result, measures such as adding a cracked or hydrogenated and desulfurized heavy gas oil to the light gas oil fraction, or increasing the production of blend oils which can be added to straight run light gas oil fractions are being considered.
In the case of blend oils which can be added to a straight run light gas oil fraction, light cycle oil having a specific boiling point range obtained from a fluid catalytic cracker is drawing considerable attention as a new blend oil for light gas oil.
However, because the light cycle oil contains a large amount of aromatic hydrocarbons, adding the light cycle oil with these characteristics directly to the straight run light gas oil fraction causes the cetane index of the thus obtained light gas oil to be lowered substantially.
Furthermore, in terms of the standards for aromatic hydrocarbon content within light gas oil fuel, it is anticipated that, in the future, a further reduction of the amount of aromatic hydrocarbons included in light cycle oil to below current levels will be required by law. This is because air pollutants such as particulates in the exhaust gas of diesel engines which contains aromatic hydrocarbons, and specifically the particulate matter which occurs due to the incomplete combustion of a portion of the aromatic hydrocarbons, cause environmental problems. Strict regulations are already in place in Sweden and in California, USA regarding the content of aromatic hydrocarbons in light gas oil.
In order to use the light cycle oil as a blend oil, it is desirable that the aromatic hydrocarbon content be reduced by performing catalytic hydrogenation on the light cycle oil. The sulfur compound content of light cycle oil is low compared with straight run light gas oil fractions, but the hydrogen sulfide produced during hydrogenation of the sulfur compound in there oils may cause a deterioration in activity by inhibiting the hydrogenation of the aromatic hydrocarbons and poisoning active sites of the hydroprocessing catalyst. Consequently, a hydrogenation catalyst for light cycle oil must have high hydrogenation activity and sulfur resistance with respect to aromatic hydrocarbons, and also have desulfurization capabilities.
Among hydrogenation catalysts, catalysts wherein a Group VIII metal is supported by a carrier such as alumina generally have high hydrogenation activity and are effective catalysts, but they suffer in that they deactivate early by being poisoned by the sulfur compounds and the like in the hydrocarbon oils. In order to overcome this problem, an attempt to perform hydrogenation using a catalyst containing zeolite in the carrier is described in Japanese Patent Publication No. Toku Kai Sho 64-66292, and Japanese Patent Publication No. Toku Hyo Hei 8-509999. However, although zeolite is a catalyst with high hydrocracking activity, in hydroprocessing, a hydrocracking occurs at the same time. Because the liquid yield of the light gas oil fraction decreases if a hydrocracking occurs during the hydroprocessing of light cycle oil, it is necessary to suppress hydrocracking activity as much as possible. In addition, the catalyst is poisoned by the high concentration of sulfur compounds and the like contained in the crude oil, and the hydrogenation activity with respect to the aromatic hydrocarbons remains unsatisfactory.
Furthermore, an attempt to perform hydroprocessing using a catalyst comprising a crystalline clay mineral having silicon and magnesium as its main components is disclosed in Japanese Patent Publication No. Toku Kai Hei 8-283746. However, while this method did have the effect of suppressing hydrocracking and raising the yield of the oil product, the hydrogenation activity with respect to the aromatic hydrocarbons remains unsatisfactory.
Generally, catalysts are formed with either comparatively large pores of greater than several dozen nm, or conversely with small pores of less than several dozen nm, and/or with a combination of comparatively large pores of greater than several dozen nm and small pores of less than several dozen nm. The balance of these pore capacities has a large influence on the targeted hydrogenation activity.
The pore characteristics are measured using a mercury porosimetry method for sizes ranging from 4 to 46800 nm, a nitrogen adsorption-DH method for sizes ranging from 2 to 200 nm, and a nitrogen adsorption-t-plot method for sizes ranging from 0.7 to 2 nm. The nitrogen adsorption-DH method and the nitrogen adsorption-t-plot-method are analysis methods based on adsorption isotherms obtained by nitrogen adsorption measurements, and the term xe2x80x9cmeasurementxe2x80x9d in the present specification includes obtaining physical properties by means of this type of analysis.
The pore characteristics of the catalyst, for example, the total volume of pores sized from 0.7 to 2 nm contained in 1 g of catalyst is referred to as xe2x80x9cthe 0.7 to 2 nm pore volumexe2x80x9d and is expressed in units of ml/g.
An object of the present invention is to provide a catalyst which resolves the problems described above associated with conventional catalysts, which is suitable for hydrogenation of hydrocarbon oils containing sulfur compounds and the like, and particularly light gas oil fractions, to reduce the aromatic hydrocarbon content, and which has high resistance to sulfur compounds, high hydrogenation activity, and moreover produces an oil product with a high liquid yield.
A hydrogenation catalyst of the present invention is a hydrogenation catalyst for hydrocarbon oils containing aromatic hydrocarbons, wherein the catalyst comprises a carrier and an active metal, and the pore characteristics of the catalyst are such that the volume of pores with a pore size of at least 4 nm as measured by a mercury porosimetry method is within a range from 0.3 to 0.6 ml/g, the volume of pores with a pore size of at least 200 nm is no more than 0.05 ml/g, the volume of pores with a pore size from 0.7 to 2 nm as measured by a nitrogen adsorption-t-plot method is within a range from 0.2 to 0.3 ml/g, and the volume of pores with a pore size from 2 to 4 nm as measured by a nitrogen adsorption-DH method is within a range from 0.15 to 0.2 ml/g.
Preferably the hydrocarbon oil contains 80 weight percent or more of a fraction with a boiling point of 170 to 390xc2x0 C.
Preferably the hydrogenation catalyst for hydrocarbon oils containing aromatic hydrocarbons comprises a carrier and an active metal, wherein the carrier is composed of silica-magnesia, the active metal is a noble metal selected from the group VIII of the periodic table, and the magnesia content of the silica-magnesia is within a range from 25 to 50 weight percent, calculated in terms of the metal oxide.
Preferably the proportion of the noble metal selected from the group VIII of the periodic table is within a range from 0.1 to 2 weight percent, calculated in terms of the metal.
In the hydrogenation catalyst for hydrocarbon oils containing aromatic hydrocarbons, preferably the catalyst comprises a carrier and an active metal, and the effective pore size distribution of the catalyst is composed of pore sizes within a range from 4 to 200 nm, and pore sizes within a range from 0.7 to 4 nm, wherein the volume of pores with a pore size in the range from 4 to 200 nm is 0.3 to 0.6 ml/g, and the volume of pores with a pore size in the range from 0.7 to 4 nm is 0.35 to 0.5 ml/g.
The inventors of the present invention, as a result of investigating inorganic oxides which form the substrate of a catalyst, discovered a silica-magnesia composition for use as a carrier material, and investigated the performance of a catalyst formed by the conventional process of supporting a noble metal from the group VIII of the periodic table by this silica-magnesia composition. In addition, the inventors discovered that in terms of the composition ratio of the silica-magnesia compound, a preferred specific range exists which is suitable for lowering the amount of aromatic hydrocarbons in the light gas oil fraction by hydrogenation and is satisfactorily resistant to sulfur hydrocarbons and the like, and also discovered that a suitable range exists with regard to the amount of active metal, and proposed these findings in Japanese Patent Application No. Toku Gan Hei 10-356347. In addition, the inventors of the present invention developed the present invention as a result of conducting intensive research into lowering the amount of aromatic hydrocarbons. Moreover, the silica-magnesia composition utilizes an amorphous material.
In other words, the present invention provides a hydrogenation catalyst for the aromatic hydrocarbons included in hydrocarbon oils. The catalyst has a silica-magnesia composition as the carrier, and comprises a silica-magnesia oxide carrier with a magnesia content within a range from 25 to 50 weight percent calculated in terms of the metal oxide, to which a noble metal selected from among the group VIII metals of the periodic table has been added as the active component. In addition, the pore characteristics of the catalyst are such that the volume of pores with a pore size of at least 4 nm as measured by a mercury porosimetry method is within the range from 0.3 to 0.6 ml/g, the volume of pores with a pore size of at least 200 nm is no more than 0.05 ml/g, the volume of pores with a pore size from 0.7 to 2 nm as measured by nitrogen adsorption-t-plot method is within the range from 0.2 to 0.3 ml/g, and the volume of pores with a pore size from 2 to 4 nm as measured by nitrogen adsorption-DH method is within the range from 0.15 to 0.2 m/g.
It is preferable that the hydrocarbon oil contains a fraction with a boiling point of 170 to 390xc2x0 C. by an amount of 80 weight percent or more.
It is preferable that the hydrogenation catalyst for hydrocarbon oils containing aromatic hydrocarbons comprises a carrier and an active metal, wherein the carrier is formed from silica-magnesia, the active metal is a noble metal selected from the group VIII of the periodic table, and the magnesia content of the silica-magnesia is within a range from 25 to 50 weight percent, calculated in terms of the metal oxide. Moreover, the silica-magnesia oxide carrier is produced using a silica-magnesia hydrate gel as a basic raw material.
It is preferable that the proportion of the noble metal selected from the group VIII of the periodic table is within a range from 0.1 to 2 weight percent, calculated in terms of the metal.
A catalyst of the p resent invention is prepared by adding a salt solution of the noble metal selected from the group VIII of the periodic table to the carrier comprising a silica-magnesia hydrate gel and/or silica-magnesia oxide carrier, using either a co-mixing method or an impregnation method, and then following drying, performing a calcination. The silica-magnesia hydrate gel becomes silica-magnesia oxide carrier through the calcination.
Specifically, the salt solution of the noble metal selected from the group VIII of the periodic table is added to the silica-magnesia hydrate gel which has a magnesia content, calculated in terms of the metal oxide, of between 25 and 50 weight percent, and the mixture is then kneaded and extruded, and after drying, is calcined (co-mixing method). Alternatively, a silica-magnesia oxide carrier obtained by kneading and extruding the silica-magnesia hydrate gel with a magnesia content, calculated in terms of the metal oxide, of between 25 and 50 weight percent, drying and subsequent calcination is impregnated with a salt solution of the noble metal selected from the group VIII of the periodic table, and then after drying, is subjected to calcination (impregnation method).
Common hydrolysis methods for manufacturing the silica-magnesia hydrate gel with a magnesia content, calculated in terms of the metal oxide, of between 25 and 50 weight percent include a coprecipitation method, a deposition method, and a sol-gel process, although the coprecipitation method is preferred. For example, hydrolysis is performed using a method wherein a sodium silicate aqueous solution, and a magnesium chloride aqueous solution with an amount of magnesium, calculated in terms of the oxide MgO, within a range from 25 to 50 weight percent, are added dropwise concurrently or approximately concurrently into a reaction vessel at a hydrolysis temperature within a range from 40xc2x0 C. to 60xc2x0 C., and the thus produced silica-magnesia hydrate slurry is then filtered, washed, and filtered again to obtain a silica-magnesia hydrate gel.
In the present invention, the reason the magnesia content in the silica-magnesia oxide carrier, calculated in terms of the metal oxide, is limited to a value within the range from 25 to 50 weight percent is that outside this range, the hydrogenation catalyst does not function sufficiently well to fulfill the object of the present invention, because the amount of solid acid in the silica-magnesia reduces and/or the amount of solid base increases.
Furthermore, the reason the reaction temperature during hydrolysis is set to a value within the range from 40xc2x0 C. to 60xc2x0 C. is that outside this temperature range, the requirements for the pore characteristics for the hydrogenation catalyst of the present invention cannot be satisfied.
Examples of the silica raw material which can be used in the manufacture of the aforementioned silica-magnesia hydrate gel include water soluble salts such as a No. 1 sodium silicate solution, a No. 2 sodium silicate solution and a No. 3 sodium silicate solution. Furthermore, water soluble salts such as magnesium chloride, magnesium sulfate, magnesium nitrate and magnesium acetate can be used as the magnesia raw material.
Next, a plastic substance obtained by adding the salt solution of the noble metal selected from the group VIII of the periodic table to the silica-magnesia hydrate gel so that the metal component, calculated in terms of the metal, is from 0.1 to 2 weight percent and subsequent kneading, or a plastic substance obtained by kneading the aforementioned silica-magnesia hydrate gel, is extruded into the desired shape, and after drying, is calcined.
The shape of the extruded product may be any desired shape such as cylindrical, two leaf, four leaf, or spherical.
Provided the extruded object is dried evenly, drying should not present any particular problems, and for reasons of efficiency and simplicity, the extruded object should be dried at a temperature within a range from 80xc2x0 C. to 120xc2x0 C. Furthermore during calcination, because changes may occur such as an agglomeration or a phase change of the active component, the calcination temperature should normally be between 350xc2x0 C. and 600xc2x0 C., and preferably between 400xc2x0 C. and 500xc2x0 C. If the calcination temperature is below 350xc2x0 C. an oxide state is not attained, and if the calcination temperature exceeds 600xc2x0 C., the specific surface area decreases markedly.
In the present invention, the active component or the active metal is selected from metals such as ruthenium, rhodium, palladium or platinum from the group VIII of the periodic table, and a combination of palladium and platinum is especially favorable.
The reason the amount of the active component added, or the amount of the active metal supported is within the range, calculated in terms of the metal, from 0.1 to 2 weight percent relative to the weight of the catalyst is because an amount of less than 0.1 weight percent is too low for the effects caused by the active metal to manifest, whereas an amount exceeding 2 weight percent offers no further improvement in catalytic activity.
The metal salt of the noble metal used in the present invention may be any salt provided that it is a water soluble salt, and suitable examples include a nitrate, a chloride, an acetate or an ammine complex.
Examples of support methods include ion exchange methods, impregnation methods, gas phase methods and co-mixing methods, although the impregnation method and/or the co-mixing method, which are the most representative conventional catalyst preparation methods, are the most convenient. Furthermore, after being supported on the carrier, drying and calcination are then performed to fix the active metal component to the metal oxide carrier.
The pore characteristics of the hydrogenation catalyst obtained in this manner are preferably such that the volume of pores with a pore size of at least 4 nm as measured by the mercury porosimetry method is within a range from 0.3 to 0.6 ml/g, the volume of pores with a pore size of at least 200 nm is up to 0.05 ml/g, the volume of pores with a pore size from 0.7 to 2 nm as measured by the nitrogen adsorption-t-plot method is within a range from 0.2 to 0.3 ml/g, and the volume of pores with a pore size from 2 to 4 nm as measured by the nitrogen adsorption-DH method is within a range from 0.15 to 0.2 ml/g. The nitrogen adsorption-t-plot method is suitable for measuring the range between 0.7 to 2 nm. Furthermore, the nitrogen adsorption-DH method is capable of measuring pore sizes from 2 to 200 nm, although in this application this is limited to pore sizes from 2 to 4 nm. Furthermore, it is preferable that the specific surface area measured using the nitrogen adsorption-BET method is within a range from 350 to 460 m2/g.
The volume of pores with a pore size of at least 4 nm as measured by the mercury porosimetry method is kept within the range from 0.3 to 0.6 ml/g, because at less than 0.3 ml/g, the resistance to diffusion of the hydrocarbon oil (reaction material) through the pores of the catalyst is large, and it becomes difficult for the hydrocarbon oil (reaction material) to penetrate to the inside of the pores, and consequently the dearomatizing rate, the desulfurization rate and the denitrogentation rate deteriorate. Conversely, it is also preferable not to exceed 0.6 ml/g, because in addition to the catalyst losing its usefulness as an industrial catalyst due to a deterioration in the crushing strength of the catalyst, the stability of the catalytic activity also deteriorates, and the catalyst deactivates prematurely.
Furthermore, the volume of pores with a pore size of at least 200 nm as measured by the mercury porosimetry method is restricted to no more than 0.05 ml/g because at volumes exceeding 0.05 ml/g, in addition to the catalyst losing its usefulness as an industrial catalyst due to a deterioration in the crushing strength of the catalyst, the stability of the catalytic activity deteriorates, and the catalyst deactivates prematurely, which is undesirable.
In addition, the volume of pores with a pore size in the range from 0.7 to 2 nm as measured by the nitrogen adsorption-t-plot method are kept within the range from 0.2 to 0.3 ml/g for the following reasons. Namely, if the volume of pores with a pore size in the range from 0.7 to 2 nm as measured by the nitrogen adsorption-t-plot method is less than 0.2 ml/g, the supported active metal agglomerates more easily, the dispersability of the active metal particles deteriorates, and the dearomatizing rate, the desulfurization rate and the denitrogentation rate fall. Conversely, if the volume of pores with a pore size from 0.7 to 2 nm is larger than 0.3 ml/g, a hydrocracking is more likely to occur, coke deposits form inside the pores, and the catalyst deactivates prematurely.
Furthermore, the volume of pores with a pore size in the range from 2 to 4 nm as measured by the nitrogen adsorption-DH method is kept within the range from 0.15 to 0.2 ml/g in order to achieve a balance between the volume of pores with a pore size in the range from 0.7 to 2 nm and the volume of pores with a pore size in the range from 4 to 200 nm which is favorable for hydrogenation activity. In other words, it is clear from the volume of pores with a pore size between 0.7 and 4 nm as measured by the nitrogen adsorption-t-plot method and the nitrogen adsorption-DH method, and the volumes of pores with a pore size of at least 4 nm and at least 200 nm as measured by the mercury porosimetry method, that there is a depression in the pore distribution within the range from 2 to 4 nm.
It is preferable that the hydrocarbon oil contains 80 weight percent or more of a fraction with a boiling point of 170 to 390xc2x0 C. Light gas oil, kerosene, and jet fuel are examples of hydrocarbon oils that fall within this range.
The crushing strength of an industrial catalyst carrier varies according to the shape of the catalyst, but generally, a value of at least 1.0 kg/mm is required for a 1.5 mm cylindrical catalyst.
The specific surface area as measured by the nitrogen adsorption-BET method is set within the range from 350 to 460 m2/g because if the specific surface area is either too small or too large, the catalytic hydrogenation does not proceed efficiently.
It is thought that the catalyst of the present invention has high hydrogenation activity for aromatic hydrocarbons contained in hydrocarbon oils and yet is highly resistant to poisoning by sulfur hydrocarbons and the like because the targeted reaction proceeds very efficiently due to the specific pore structure and high specific surface area of the catalyst.
In the pore characteristics of the present invention, the volume of pores with a pore size from 0.7 to 2 nm is calculated by the nitrogen adsorption-t-plot method (Coloid Interface Sci., 21, 405 (1996)), the volume of pores with a pore size from 2 to 4 nm is calculated by the nitrogen adsorption-DH method (Kelvin Equation), and the specific surface area is calculated by the nitrogen adsorption-BET method. In addition, the aromatic hydrocarbons in the oil processed to evaluate the performance of the catalyst is determined using a High Performance Liquid Chromatograph (manufactured by Shimazu Corporation), the sulfur content is determined using a Total Sulfur Analyzer (made by Mitsubishi Chemical Corporation (Ltd.)), and the nitrogen content is determined using a Total Nitrogen Analyzer (made by Mitsubishi Chemical Corporation (Ltd.)).
As follows, the present invention is described in greater detail with reference to a series of working examples and comparative examples, although the present invention is in no way limited to the examples presented.